The correct answer is option c.
calculating the length of chicken eggs in millimeters.
In order to calculate the data correctly, the standard measuring units should be used. the standard units are the ones, which are same world wide and do not vary according to person or location. The appearance of the mouse may vary depending on the habitat of the mouse and the type of mouse used. the steps and length of the hand may vary person to person, depending on his/her physical dimensions. But, the millimeter would be a millimeter always, it is same at every site, hence, it would give the accurate measurement.
